634 pbuf_header(p, -(ptrdiff_t)((uint8_t*)pdu - (uint8_t*)p->payload) - sizeof(coap_pdu_t)); /* FIXME hack around udp_sendto not restoring; see http://lists.gnu.org/archive/html/lwip-users/2013-06/msg00008.html. for udp over ip over ethernet, this was -42; as we're doing ppp too, this has to be calculated generically */